Many people these days toss around the term ‘observer effect’ without really knowing what it is or what its full implications are.
Probably the person most responsible for examining this question was an American physicist called John Archibald Wheeler.
Wheeler, a protégé of Danish physicist Niels Bohr, was fascinated by what became known as the Copenhagen Interpretation, after the place where Bohr, and his brilliant protégé, the German physicist Werner Heisenberg, formulated the likely meaning of their extraordinary mathematical discoveries.
Bohr and Heisenberg realized that atoms are not little solar systems of billiard balls but something far more messy: a tiny cloud of probability.
As the founders of quantum theory first discovered in the early part of the twentieth century, subatomic particles like electrons or photons by themselves aren’t an actual anything yet.
Every subatomic particle is not a solid and stable thing, but instead exists in many states at once, in a state of pure potential — what is known by physicists as a ‘superposition’, or sum, of all probabilities.
Scientists only allow that an electron ‘probably’ exists when they pin it down and take a measurement, at which point those multiple states of being collapse and the electron settles down into a single state of being.
The fact that this occurs only when the particle is measured or observed suggests a staggering possibility to many scientists: that the role of the scientist himself — or in real life, the role of living consciousness — somehow is the influence on the smallest elements of life that turns the possibility of something into something real.
A new double-slit experiment
Wheeler wanted to test this with a variation of the famous double-slit experiment in quantum physics, a variation of an experiment with light first created by Thomas Young, a British physicist of the nineteenth century.
In Young’s experiment, a beam of pure light is sent through a single hole, or slit, in a piece of cardboard, then passes through a second screen with two holes before finally arriving at a third, blank screen.
In Young’s experiment, the light passing through the two holes forms a zebra pattern of alternating dark and light bands on the final blank screen. If light were simply a series of particles, two of the brightest patches would appear directly behind the two holes of the second screen – as a pattern of individual particles.
However, the brightest portion of the pattern is halfway between the two holes, caused by the combined amplitude of those waves that most interfere with each other. From this pattern, Young was the first to realize that light beaming through the two holes spreads out in overlapping waves.
A modern variation of the experiment fires off single photons through the double slit using a gadget called an interferometer. These single photons also produce zebra patterns on the screen, demonstrating that even single units of light travel as a smeared-out wave with a large sphere of influence.
Twentieth-century physicists went on to use Young’s experiment with other individual quantum particles, and held it up as proof that quantum physics has Through-the-Looking-Glass properties: quantum entities acted wavelike and travel though both slits at once.
Since you need at least two waves to create such interference patterns, the implication of the experiment is that the photon is somehow mysteriously able to travel through both slits at the same time and interfere with itself when it reunites.
Nevertheless, there is a catch to this experiment: when the experimental apparatus has a particle detector on it to discover which slit the photon went through, it changes the outcome of the experiment. Instead of being wave-like, the photon acts like a particle and is detected as definitely traveling through one of the two slits.
Rather than creating an interference pattern, it creates a definite particle pattern on the screen.
So when the particle detector is turned on, rather than a smeared out, uncongealed wave, the photon acts like a solid particle: it has come into being. At this point, it collapses to a single entity, goes through only one of the slits and enables you to track its path.
Delayed choice experiment
In 1978, when Wheeler was pondering the meaning of this experiment — which seemed to place an emphasis on whether the photons were detected or not — he wondered whether timing was important – whether it mattered at which point the photon is observed or measured.
He devised a famous thought experiment called the Delayed Choice Experiment, in which a particle detector is delayed so that the photon’s path only gets detected after it has gone through the slits.
Think of a photon which has already passed through the slits and is traveling toward the back walls. There are three possible routes for the photon: the left slit, the right slit or both slits at the same time, and at this stage, we don’t know which route it has taken.
Wheeler imagined that the apparatus includes a highly mobile detector screen, which can either be either removed at this point or left in place. If the screen is removed, two telescopes are revealed, each one trained on one of the slits. If the screen is removed, the telescopes be able to see and record a little flash of light as the photon traveled through one of the slits and so be able to detect the path of the photon through one or the other slit.
In this experiment, the observer has ‘delayed his choice’ of whether he wants to observe the path of the photon (via the telescopes) or not until after the photon has presumably made its decision to go through one slit, the other slit or both.
According to Wheeler’s ingenious mathematics, the path of the photons entirely depends upon whether they are observed or not.
Astonishingly, if we remove the screen and the telescopes record the path of the photons – even after the photon has passed through the double slits – we get a distribution pattern consistent with the kind of pattern we’d get if particles were going through one or the other of the two slits, but not both.
If the screen is up, the photons remain in a state of superposition and go through both slits.
Observation – backward in time?
The remarkable aspect of this experiment of course, is that timing is irrelevant: even after the event has occurred and the photon has gone through one or both slits, the presence or absence of the screen — that is the presence or absence of observation — determines its final outcome.
So the implications are that observation, even after the fact, determines the final outcome.
The observer entirely controls whether that which is observed comes into being – at any point in time.
In the words of Wheeler’s protégé, the famous physicist Richard Feynman, the role of the observer in quantum physics was the ‘mystery which cannot go away’.
Nevertheless Wheeler’s idea remained an intriguing feat of mathematics until 2007 when Jean-François Roch and his and his colleagues at the Ecole Normale Supérieure de Cachan in France found a way to carry out the experiment Wheeler had imagined thirty years ago.
At its most elemental, physical matter not only isn’t an anything yet, but remains something indeterminate until our consciousness becomes involved with it. The moment we look at an electron or take a measurement, it appears that we help to determine its final state. The most fundamental relationship of all may be matter and the consciousness that observes it.
However, what is most breathtaking about Wheeler’s discoveries and the proving by Roch and his fellows is the implications about the irrelevancy of time.
As Wheeler once noted in 2006, two years before he died: “We are participators in bringing into being not only the near and here but the far away and long ago.” In his fertile imagination, he even imagined the entire universe as one giant wave in need of observation to have brought it into being.
In this instance, perhaps the observer will turn out to be God.